sedimentary
Chalcedony (Agate Pebble)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs); Color: Waxy white to light gray with dark speckles; Luster: Waxy to dull; Structure: Microcrystalline quartz; Specific Gravity: 2.6-2.64.
- Hardness
- 6
- Color
- Waxy white to light gray with dark speckles
- Luster
- Waxy to dull
Identified More sedimentary →
Explore Chalcedony (Agate Pebble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 (Mohs); Color: Waxy white to light gray with dark speckles; Luster: Waxy to dull; Structure: Microcrystalline quartz; Specific Gravity: 2.6-2.64.
Formation & geological history
Formed as a chemical precipitate in cavities of volcanic rocks or sedimentary environments. This specific specimen shows signs of water erosion (alluvial), likely deposited in a stream or river bed during the Quaternary period.
Uses & applications
Commonly used for lapidary work (tumbling/polishing), jewelry (beads), and as an industrial abrasive. Many small specimens like this are collected as decorative pebbles.
Geological facts
Chalcedony is a cryptocrystalline form of silica. The name 'Agate' is specifically used when it shows banding, though many river pebbles are unbanded chalcedony. It was highly prized in antiquity for cylinder seals.
Field identification & locations
Identify by its waxy luster and inability to be scratched by a steel knife. Common in gravel pits, riverbeds, and beaches across North America and Europe. Look for translucency when held to a light source.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Brown Sandstone (River Rock)
Arenite
sedimentary
Mudstone
Argillite / Siliciclastic sedimentary rock
sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary